1. Field of the Invention
The invention relates to a method for the extraction of intact liquid samples, in particular, from a well sunk into the ground, by submersion of a compressible hollow flexible body fitted in supporting means which, subsequent to submersion to the sample extraction depth, is acted upon to effect liquid entry through an inlet, as well as a sample extractor for performing the method.
2. Description of Related Art
Such a sample extractor is known from U.S. Pat. No. 4,461,186 which comprises a sterile flexible body in the form of a tubular bag, the openings of which are fitted by means of compression rings to two rigid endpieces, the upper of which comprising an inlet being releasably fitted to the console of a sample extractor, and the lower being fitted in the vertically displaceable console of the sample extractor which is forced away from the upper endpiece by elastic means. The lower endpiece comprises a vertical pin projecting up into the bag volume and fitting into said inlet in such a manner that the endpieces are placed at a certain distance from another in the starting position, corresponding to the length of the pin, whereby air will be present in the bag at the commencement of sample extraction.
The inlet in the upper endpiece is covered by a hose which is connected to a glass tube fixed in a crunching mechanism. The sample extraction is activated in that a weight is dropped when the sample extracted with a bag fitted is placed at the desired depth, said weight falling on the crunching mechanism which fractures the glass tube whereby the inlet opening is uncovered, and liquid may flow through it. The same mechanism is further connected to a release mechanism which releases the lower endpiece so that this, due to the influence of the downward directed elastic means, is displaced such that sample material is sucked through the inlet in the upper endpiece. The sample extraction is terminated in that the lower endpiece acts on a spring loaded valve via a rod-and-spring which blocks the inlet in the upper endpiece. Subsequently the sample extractor is hoisted up and the fluid sample collected in the bag volume may be removed from the sample extractor along with the endpieces. The sample extraction hence occurs using the bellows principle, where an elastic influence on one endpiece away from the upper, fixed endpiece causes surrounding fluid to be sucked into the bag volume.
This known sample extractor would be adapted to use in extraction of samples in predetermined depths where the requirements for the method used are not particularly rigid, i.e., where it is known beforehand that the subsequent results of analyses are reasonably removed from the detection limit of the substances in question. Examples might be the extraction of water samples in marine areas in the sea or in lakes, and in wells and large-diameter wells, where sufficient room is available for the submersion of the complete sample extraction equipment.
The extraction of fluid or water samples in order to detect substances endangering the environment in the course of evaluation of, e.g., the extent and distribution of ground water pollution is commonly performed. The extraction of the water samples directly at the filter of a well as well as in the water claiming area, where the water samples are extracted in pipes placed in the ground for this purpose.
Since the concentrations of the substances endangering the environment in, e.g., drinking water wells and water claiming areas are often near the detection limit, it is of a large importance that the samples are extracted in such a way that it is representative of the actual water quality in a given level at the particular sample extraction site.
Hence rigid requirements are put on the cleanliness of the equipment used for the sample extraction, while it is of a large importance that the samples may be extracted in different depths in the well, such that these are representative, and to enable the extraction of samples which are non-oxidised and which have not been subjected to atmospheric air, whereby gasses which may have been dissolved in the water sample might escape.
It would be impossible to use the sample extractor described in U.S. Pat. No. 4,461,186 for the extraction of the mentioned intact liquid samples which have to be analysed for substances occurring in concentrations very close to the detection limit. There are several reasons for this, e.g., atmospheric air will be present in the bag volume at commencement of the sample extraction. Lowering of the sampling equipment will cause turbulence and mixing of layers possibly occurring within the well, due to the construction and size of the equipment. This situation is further aggravated by dropping weight in order to crunch the glass tube which initiates the sample extraction.
Alternatively intact water samples may be extracted by means of a vacuum pump situated on the ground by the well, which sucks the water sample into a sample bottle. However, it may be difficult to determine the precise depth from which the sample is pumped, and there may be doubts as to possible contamination by substances present in the higher water layers in the well. Furthermore, there remains the fact that the pumped water sample cannot avoid, however briefly, to be in contact with air when it is fed to a sample container, which is undesired as described above. The problem with using a vacuum pump is furthermore that it hardly functions at depths exceeding 10 m. However, in order to solve this problem, pumps are known which are so small that they may be sunk into the well and pump the samples up. If such a pump is to be used in other locations, it must be cleaned first which is a time consuming and hence cost creating work which sometimes makes one use one pump per well which is costly in acquisition but often necessary, but even here remains the problem of the sample""s contact with air.
It is the purpose of the present invention to provide a method for the extraction of intact fluid samples, in particular from a well sunk into the ground, by submersion of a compressible hollow flexible body fitted in supporting means comprising an inlet which, subsequent to submersion to the sample extraction depth, is filled with fluid, and a sample extractor to perform the method which alleviates the disadvantages concerning the use of the known pumps and which permits the extraction of intact and representative water samples without allowing the extracted samples to contact the atmosphere during sample extraction.
It has been realised in the invention that this purpose is obtainable in that the hollow flexible body is held in support means in the form of a pressure vessel during lowering to the desired sample extraction depth and filly compressed by means of a pressurised gas inside the pressure vessel, whereupon the pressure in the pressure vessel is caused to change in such a way that a surrounding fluid seeps into the hollow flexible body.
Due to the fact that the hollow flexible body is fully compressed until the seeping of the fluid is effected by releasing the pressure in the pressure vessel it is obtained that the collected fluid sample does not contact the atmosphere which means that the sample remains intact and hence un-influenced, until it is analysed.
For the performance of the methods, a sample extractor is provided of the kind in which the support means are constituted by a leak-proof container in which is placed the compressible hollow flexible body in the form of a bag of a suitable clean and resistant material, the open end of which is connected to the inlet in an air- and fluid tight manner, and which container is connected to a hose, at the other end of which means are provided for controlling the pressure between the wall of the container and the outside of the bag, which inlet is preferably provided at a bottom end of the container, viz. a removable tightly fitting plug, to which is fitted the flexible body and which has a through passage with an embedded one-way valve.
It is hereby possible to lower the sample extractor to the preferred depth in, e.g., a well, and here extract an intact fluid sample by equalising the pressure in the pressure vessel at the valve, whereby the surrounding liquid pressure in the well will cause a flow of liquid through the one-way valve and into the bag.
In order to avoid the collection of liquid in the gap of the one-way valve at the valve seat during the lowering of the sample extractor to the desired sample extraction depth, the one-way valve seat is oblong and conical, and the plunger is similarly inverse oblong and fitting to the valve seat, and the valve seat furthermore communicates with a preferably oblique passage in the longitudinal direction in the lower end of the plug, so that the lower part of the oblong conical plunger projects into the passage.
The functioning of this embodiment of the one-way valve and the plug is that there is no cavity in the opening of the one-way valve in which liquid may collect, because the plunger fills the opening of the one-way valve completely. Furthermore the embodiment of the one-way valve ensures a very large sealing surface between the valve seat and the plunger. Furthermore the oblique disposition of the passage contributes to ensuring that the liquid collected in the bag via the one-way valve is representative for the level below the surface of the liquid to which the sample extractor has been lowered, as during the lowering below the water table there will be a flow of liquid through the passage, and hence the liquid present in the passage will always come from the liquid present at the level to which the sample extractor has been lowered.
In order to prevent the influence of liquid pressure on the plunger of the one-way valve, the lower part of the plug may be of a conical shape, hereby the passage is protected and also the end of the plunger projecting into it, however without blocking the passage.
In order to ensure that there is no air in the bag during the lowering of the sample extractor and during the sample extraction, the upper part of the plunger of the one-way valve, around which the bag is fitted may be rounded and mutually adjusted in such a way that there are no air pockets present between the mouth of the bag and the top of the plug and said plunger in the compressed condition of the bag during lowering for the extraction of a liquid sample and such that turbulent liquid flow via the one-way valve into the volume of the bag is prevented.
In order to remove minute undesired amounts of air between the water level in the liquid sample collected in the bag and the top of the bag, the bag may be fitted with a valve at its closed end for the expulsion of air before packing and sending the sample for analysis.
In order to enable the control of the pressure of the fluid which compresses the body in the sample extractor, the pressure hose between the container and the valve may be fitted with a double tee fitted with a pressure indicator, a one-way valve with a fitting for connecting to a pressure source.
In order to enable the use of the sample extractor for the extraction of samples at small distances below a water table, the double tee may be connected to a valve for the control of pressure, a pressure indicator and the double tee may optionally be connected via a valve to a source of pressure and/or vacuum, whereby the pressure chamber may respectively be supplied with pressure for complete compression of the bag during lowering and vacuum during the actual sample extraction, whereby liquid is sucked into the bag.
It should be mentioned that the method according to the invention as well as the sample extractor for performing the method may also be used for sample extraction in other connections than for the extraction of samples in a well sunk into the ground. The invention is furthermore suitable for the extraction of intact samples in, e.g., lakes, open wells, tanks, including oil separators.
The invention is explained in greater detail in the following with reference to the accompanying drawings.